Ultrasonic imaging has found use in accurate measurement of structures of the eye such as, for example, the cornea and lens capsule. Such measurements provide an ophthalmic surgeon valuable information that can be used to guide various surgical procedures for correcting refractive errors such as LASIK and lens replacement. They also provide diagnostic information after surgery has been performed to assess the geometrical location of corneal features such as the LASIK scar and lens features such as lens connection, position and orientation. This allows the surgeon to assess post surgical changes in the cornea or lens and to take steps to correct any problems that develop.
Except for on-axis measurements, dimensions and locations of eye components behind the iris cannot be fully determined by optical means. Ultrasonic imaging in the frequency range of about 5 MHz to about 80 MHz can be applied to make accurate and precise measurements of structures of the eye, such as the cornea, lens capsule, lens ciliary muscle and the like.
Ultrasonic imaging has been used in corneal procedures such as LASIK to make accurate and precise images and maps of cornea thickness which include epithelial thickness, Bowman's layer and images of LASIK flaps. These images have a resolution of a few microns.
New procedures such as implantation of accommodative lenses may provide nearly perfect vision without spectacles or contact lenses. Implantation of accommodative lenses requires precision measurements of, for example, the position and width of the natural lens for successful lens powering and implantation. Ultrasonic imaging can be used to provide the required accurate images of the natural lens especially where the zonules attach the natural lens to the ciliary body which is well off-axis and behind the iris and therefore not readily accessible to optical imaging.
Other new procedures such as implantation of stents in or near the suprachoroid space may provide part or all of a treatment for glaucoma. Ultrasonic imaging can be used to provide the required accurate images in the corner of the eye between the sclera and the iris (in the suprachoroidal space) which is well off-axis and substantially inaccessible to optical imaging.
Such measurements can also provide ophthalmic researchers with valuable information that can be used 1) in the design of accommodative lenses, 2) provide ophthalmic surgeons with valuable information that can be used to guide various surgical procedures performed on the lens, 3) in the design of glaucoma stents, 4) provide ophthalmic surgeons with valuable information that can be used to guide placement of stents for treatment of glaucoma.
Recent advances in ultrasonic imaging have allowed images of substantially the entire lens capsule to be made. This has opened up the ability of diagnostic devices to assist in both research of lens implantation devices and strategies, and to planning, executing and follow-up diagnostics for corrective lens surgery including specialty procedures such as glaucoma and cataract treatments as well as implantation of clear intraocular lenses including accommodative lenses.
The use of ultrasonic imaging of important features of the eye for lens implantation is discussed, for example, in U.S. Pat. No. 7,048,690, which is herein incorporated by reference in its entirety. U.S. Pat. No. 7,048,690 does not include techniques for imaging the posterior surface of the lens capsule and so cannot be used to compute the volume of a lens capsule. Means for obtaining a full image of the lens capsule are disclosed in US Publication No. 2010/0,004,538 and U.S. Pat. No. 8,317,709, which are herein incorporated by reference in their entirety.
The ultrasonic system described herein is capable of accurately moving an ultrasound transducer with respect to a known reference point on a patient's head. Further improvements allow for tracking of unintended eye motions during scanning as disclosed in US Publication No. 2013/0,310,692, which is herein incorporated by reference in its entirety.
It must be appreciated that ultrasonic imaging requires a liquid medium to be interposed between the object being imaged and the transducer, which requires in turn that the eye, the transducer, and the path between them be at all times be immersed in a liquid medium wherein the acoustic impedance is substantially continuous. Concern for safety of the cornea introduces the practical requirement that the liquid medium be either pure water or normal saline water solution.
An eyepiece serves to complete a continuous acoustic path for ultrasonic scanning, that path extending from the transducer to the surface of the patient's eye. The eyepiece also separates the water in which the patient's eye is immersed from the water in the chamber in which the ultrasound transducer and guide track assembly are contained. Finally, the eyepiece provides a steady rest for the patient and helps the patient to remain steady during a scan. To be practical, the eyepiece should be free from frequent leakage problems, should be comfortable to the patient and its manufacturing cost should be low since it should be replaced for every new patient.
Another ultrasound scanning method is known as Ultrasound BioMicroscopy (UBM) which is implemented as a hand-held device that can capture anterior segment images using a transducer to emit short acoustic pulses ranging from about 20 to about 80 MHz. This type of ultrasound scanner is also called a sector scanner. The device can be used to capture reflected acoustic pulses using an open scleral shell filled with saline, which is a scleral shell filled with soft contact lens saline which is placed on an anesthetized eye and the UBM probe is held in the saline. Alternately, a special cup, known as the Prager cup may be used. This cup or bag/balloon technique using the ClearScan cover (ESI Inc., Plymouth, Minn.) utilizes a sterile, single-use water-filled bag covering the end of the UBM probe. A flexible collar, also serving as a valve to adjust internal bag pressure, secures to the ultrasound probe and creates a watertight seal. The water-filled bag conforms to the contour of the eye and inserting the probe into the bag creates positive pressure keeping the swiveling probe tip from making contact with the eye. The UBM method is capable of making qualitative ultrasound images of the anterior segment of the eye but cannot unambiguously make accurate, precision, comprehensive, measurable images of the cornea, lens or other components of the eye.
There remains, therefore, a need for integrated, closed system disposable packages that include an eye piece, a saline reservoir and associated tubing to ensure safe, precision ultrasonic scanning.